Avian species differences in susceptibility to noise exposure

Previous studies of hair cell regeneration and hearing recovery in birds af ter acoustic overstimulation have involved relatively few species. Studies of the effects of acoustic overexposure typically report high variability. Though it is impossible to tell, the data so far also suggest there may be considerable species differences in the degree of damage and the time cours e and extent of recovery. To examine this issue, we exposed four species of birds (quail, budgerigars, canaries, and zebra finches) to identical condi tions of acoustic overstimulation and systematically analyzed changes in he aring sensitivity, basilar papilla morphology, and hair cell number. Quail and budgerigars showed the greatest susceptibility to threshold shift and h air cell loss after overstimulation with either pure tone or bandpass noise , while identical types of overstimulation in canaries and zebra finches re sulted in much less of a threshold shift and a smaller, more diffuse hair c ell loss. All four species showed some recovery of threshold sensitivity an d hair cell number over time. Canary and zebra finch hearing and hair cell number recovered to within normal limits while quail and budgerigars contin ued to have an approximately 20 dB threshold shift and incomplete recovery of hair cell number. In a final experiment, birds were exposed to identical wide-band noise overstimulation under conditions of artificial middle ear ventilation. Hair cell loss was substantially increased in both budgerigars and canaries suggesting that middle ear air pressure regulation and correl ated changes in middle ear transfer function are one factor influencing sus ceptibility to acoustic overstimulation in small birds. (C) 1999 Elsevier S cience B.V. All rights reserved.